Trailer backup assist system

ABSTRACT

The trailer backup assist system has a human machine interface coupled to a controller having a setup module, a calibration module, an activation module and a control module configured to receive trailer measurements, apply trailer measurements, activate and control vehicle systems to calibrate and implement a curvature control algorithm that controls the reverse movement of the vehicle-trailer combination in a manner consistent with a driver request.

CROSS REFERENCE

This patent application is a continuation-in-part application ofco-pending U.S. Non-provisional patent application which has Ser. No.13/443,743 which was filed Apr. 10, 2012 which is a continuation-in-partapplication of co-pending U.S. Non-provisional patent application whichhas Ser. No. 13/336,060, which was filed Dec. 23, 2011, which isentitled “Trailer Path Curvature Control For Trailer Backup Assist”,which claims priority from U.S. Provisional Patent Application which hasSer. No. 61/477,132, which was filed Apr. 19, 2011, which is entitled“Trailer Backup Assist Curvature Control”, and both of which have acommon applicant herewith and are being incorporated herein in theirentirety by reference.

TECHNICAL FIELD

The disclosure made herein relates generally to driver assist and activesafety technologies in vehicles, and more particularly to a trailerbackup assist system.

BACKGROUND

It is well known that backing up a vehicle with a trailer attached is adifficult task for many drivers. This is particularly true for driversthat are untrained at backing with trailers such as, for example, thosethat drive with an attached trailer on an infrequent basis (e.g., haverented a trailer, use a personal trailer on an infrequent basis, etc.).One reason for such difficulty is that backing a vehicle with anattached trailer requires counter-steering that is opposite to normalsteering when backing the vehicle without a trailer attached and/orrequires braking to stabilize the vehicle-trailer combination before ajackknife condition occurs. Another reason for such difficulty is thatsmall errors in steering while backing a vehicle with an attachedtrailer are amplified thereby causing the trailer to depart from adesired path.

To assist the driver in steering a vehicle with a trailer attached, atrailer backup assist system needs to know the driver's intention. Onecommon assumption with known trailer backup assist systems is that adriver of a vehicle with an attached trailer wants to back up straightand the system either implicitly or explicitly assumes a zero curvaturepath for the vehicle-trailer combination. Unfortunately most of thereal-world use cases of backing a trailer involve a curved path and,thus, assuming a path of zero curvature would significantly limitusefulness of the system. Some known systems assume that a path is knownfrom a map or path planner. To this end, some known trailer backupassist systems operate under a requirement that a trailer back-up pathis known before backing of the trailer commences such as, for example,from a map or a path planning algorithm. Undesirably, suchimplementations of the trailer backup assist systems are known to have arelatively complex Human Machine Interface (HMI) device to specify thepath, obstacles and/or goal of the backup maneuver. Furthermore, suchsystems also require some way to determine how well the desired path isbeing followed and to know when the desired goal, or stopping point andorientation, has been met, using approaches such as cameras, inertialnavigation, or high precision GPS. These requirements lead to arelatively complex and costly system.

Another reason backing a trailer can prove to be difficult is the needto control the vehicle in a manner that limits the potential for ajack-knife condition to occur. A trailer has attained a jackknifecondition when a hitch angle cannot be reduced (i.e., made less acute)while continuously backing up a trailer by application of a maximumsteering input for the vehicle such as, for example, by moving steeredfront wheels of the vehicle to a maximum steered angle at a maximum rateof steering angle change. In the case of the jackknife angle beingachieved, the vehicle must be pulled forward to relieve the hitch anglein order to eliminate the jackknife condition and, thus, allow the hitchangle to be controlled via manipulation of the steered wheels of thevehicle. However, in addition to the jackknife condition creating theinconvenient situation where the vehicle must be pulled forward, it canalso lead to damage to the vehicle and/or trailer if certain operatingconditions of the vehicle relating to its speed, engine torque,acceleration, and the like are not detected and counteracted. Forexample, if the vehicle is travelling at a suitably high speed inreverse and/or subjected to a suitably high longitudinal accelerationwhen the jackknife condition is achieved, the relative movement of thevehicle with respect to the trailer can lead to contact between thevehicle and trailer thereby damaging the trailer and/or the vehicle.

Embodiments of the inventive subject matter are directed to trailerbackup assist functionality that provides for a user interface for asystem that controls curvature of a path of a trailer being backed by avehicle. More specifically, trailer backup assist functionalityconfigured in accordance with embodiments of the inventive subjectmatter provide for such trailer path curvature control by allowing adriver of the vehicle to specify a desired path of the trailer byinputting a desired trailer path curvature as the backup maneuver of thevehicle and trailer progresses. In response to such path of the trailerbeing specified by the driver, embodiments of the inventive subjectmatter control a power assisted steering system (e.g., electric powerassisted steering (EPAS) system) of the vehicle for implementingsteering angle changes of steered wheels of the vehicle to achieve thespecified trailer path. Kinematics of the vehicle and the trailer areused to determine the steering angle changes that are required forachieving the specified trailer path. Accordingly, embodiments of theinventive subject matter provide for implementation of trailer backupassist functionality in a manner that is relatively simple and thatenables use of an intuitive vehicle operator interface for specifyingtrailer path curvature control.

SUMMARY

Embodiments of the inventive subject matter are directed to a system andmethod for assisting a driver with backing an attached trailer. Thetrailer backup assist system has a human machine interface coupled to acontroller. A setup module, a calibration module, an activation moduleand a control module receive trailer measurements, apply trailermeasurements, activate and control vehicle systems to calibrate andimplement a curvature control algorithm that controls the reversemovement of the vehicle-trailer combination in a manner consistent witha driver request.

In one embodiment of the inventive subject matter a method forimplementing the trailer backup assist system comprises receivingtrailer measurements, calibrating a curvature control algorithm,activating a steering system on the vehicle, receiving a driver requestto control reverse movement of the vehicle-trailer combination accordingto a desired trailer path curvature and implementing the curvaturecontrol algorithm to provide steering commands to the steering system inresponse to the driver request. The steering commands are limited tothose provided by the curvature control algorithm.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a vehicle-trailer combination, the vehicle being configuredfor performing trailer backup assist functionality in accordance with anembodiment of the inventive subject matter embodiment.

FIG. 2 shows a preferred embodiment of the trailer backup steering inputapparatus discussed in reference to FIG. 1.

FIG. 3 shows an example of a trailer backup sequence implemented usingthe trailer backup steering input apparatus discussed in reference toFIG. 2.

FIG. 4 shows a method for implementing trailer backup assistfunctionality in accordance with an embodiment of the inventive subjectmatter.

FIG. 5 is a diagrammatic view showing a kinematic model configured forproviding information utilized in providing trailer backup assistfunctionality in accordance with the inventive subject matter.

FIG. 6 is a graph showing an example of a trailer path curvaturefunction plot for a rotary-type trailer backup steering input apparatusconfigured in accordance with the inventive subject matter.

FIG. 7 is a diagrammatic view showing a relationship between hitch angleand steered angle as it relates to determining a jackknife angle for avehicle/trailer system in reverse or backing up.

FIG. 8 shows a method for implementing jackknife countermeasuresfunctionality in accordance with an embodiment of the inventive subjectmatter.

FIG. 9 shows a Human Machine Interface (HMI) device associated with theinventive subject matter.

FIG. 10 shows a flow diagram associated with the inventive subjectmatter.

FIG. 11 shows a flow diagram of the setup module of the inventivesubject matter.

FIG. 12 shows an example of an image displayed at the HMI device inaccordance with the inventive subject matter.

Elements and steps in the figures are illustrated for simplicity andclarity and have not necessarily been rendered according to anyparticular sequence. For example, steps that may be performedconcurrently or in different order are illustrated in the figures tohelp to improve understanding of embodiments of the inventive subjectmatter.

DESCRIPTION OF INVENTIVE SUBJECT MATTER

While various aspects of the inventive subject matter are described withreference to a particular illustrative embodiment, the inventive subjectmatter is not limited to such embodiments, and additional modifications,applications, and embodiments may be implemented without departing fromthe inventive subject matter. In the figures, like reference numberswill be used to illustrate the same components. Those skilled in the artwill recognize that the various components set forth herein may bealtered without varying from the scope of the inventive subject matter.

The inventive subject matter is directed to providing trailer backupassist functionality in a manner that is relatively low cost and thatoffers an intuitive user interface. In particular, such trailer backupassist functionality provides for controlling curvature of a path oftravel of a trailer attached to a vehicle (i.e., trailer path curvaturecontrol) by allowing a driver of the vehicle to specify a desired pathof the trailer by inputting a desired trailer path curvature as thebackup maneuver of the vehicle and trailer progresses. Although acontrol knob, a set of virtual buttons, or a touch screen can each beimplemented for enabling trailer path curvature control, the inventivesubject matter is not unnecessarily limited to any particularconfiguration of interface through which a desired trailer pathcurvature is inputted. Furthermore, in the case where a steering wheelcan be mechanically decoupled from steered wheels of the vehicle, thesteering wheel can also be used as an interface through which a desiredtrailer path curvature is inputted. As will be discussed herein ingreater detail, kinematical information of a system defined by thevehicle and the trailer are used to calculate a relationship (i.e.,kinematics) between the trailer's curvature and the steering angle ofthe vehicle for determining steering angle changes of the vehicle forachieving the specified trailer path. Steering commands corresponding tothe steering angle changes are used for controlling a steering system ofthe tow vehicle (e.g., electric power assisted steering (EPAS) system)for implementing steering angle changes of steered wheels of the vehicleto achieve (e.g., to approximate) the specified path of travel of thetrailer. The trailer backup assist system automatically steers thevehicle-trailer combination as a driver uses the vehicle transmission,accelerator and brake to reverse the vehicle-trailer combination. Thedriver inputs a desired trailer curvature command by using an inputdevice such as a trailer steering knob.

Trailer backup assist functionality is directed to implementing one ormore countermeasures for limiting the potential of a jackknife conditionbeing attained between a vehicle and a trailer being towed by thevehicle while backing up. In certain embodiments of the inventivesubject matter, curvature of a path of travel of the trailer (i.e.,trailer path curvature control) can be controlled by allowing a driverof the vehicle to specify a desired path of the trailer by inputting adesired trailer path curvature as the backup maneuver of the vehicle andtrailer progresses. Although a control knob, a set of virtual buttons,or a touch screen can each be implemented for enabling trailer pathcurvature control, the inventive subject matter is not unnecessarilylimited to any particular configuration of interface through which adesired trailer path curvature is inputted. Furthermore, in the casewhere a steering wheel can be mechanically decoupled from steered wheelsof the vehicle, the steering wheel can also be used as an interfacethrough which a desired trailer path curvature is inputted. As will bediscussed herein in greater detail, kinematical information of a systemdefined by the vehicle and the trailer are used to calculate arelationship (i.e., kinematics) between the trailer's curvature and thesteering angle of the vehicle for determining steering angle changes ofthe vehicle for achieving the specified trailer path. Steering commandscorresponding to the steering angle changes are used for controlling asteering system of the tow vehicle (e.g., electric power assistedsteering (EPAS) system) for implementing steering angle changes ofsteered wheels of the vehicle to achieve (e.g., to approximate) thespecified path of travel of the trailer.

Trailer Backup Assist System

Referring to FIG. 1, an embodiment of a vehicle 100 configured forperforming trailer backup assist functionality in accordance with theinventive subject matter is shown. A trailer backup assist system 105 ofthe vehicle 100 controls the curvature of path of travel of a trailer110 that is attached to the vehicle 100. Such control is accomplishedthrough interaction of a power assisted steering system 115 of thevehicle 100 and the trailer backup assist system 105. During operationof the trailer backup assist system 105 while the vehicle 100 is beingreversed, a driver of the vehicle 100 is sometimes limited in the mannerin which he/she can make steering inputs via a steering wheel of thevehicle 100. This is because in certain vehicles the trailer backupassist system 105 is in control of the power assisted steering system115 and the power assisted steering system 115 is directly coupled tothe steering wheel (i.e., the steering wheel of the vehicle 100 moves inconcert with steered wheels of the vehicle 100). As is discussed belowin greater detail, a human machine interface (HMI) device of the backupassist system 105 is used for commanding changes in curvature of a pathof the trailer 110 such as a knob, thereby decoupling such commands frombeing made at the steering wheel of the vehicle 100. However, somevehicles configured to provide trailer backup assist functionality inaccordance with the inventive subject matter will have the capability toselectively decouple steering movement from movement of steerable wheelsof the vehicle, thereby allowing the steering wheel to be used forcommanding changes in curvature of a path of a trailer during suchtrailer backup assist.

The trailer backup assist system 105 includes a trailer backup assistcontrol module 120, a trailer backup steering input apparatus 125, and ahitch angle detecting apparatus 130. The trailer backup assist controlmodule 120 is connected to the trailer backup steering input apparatus125 and the hitch angle detecting apparatus 130 for allowingcommunication of information therebetween. It is disclosed herein thatthe trailer backup steering input apparatus can be coupled to thetrailer backup assist control module 120 in a wired or wireless manner.The trailer backup assist system control module 120 is attached to apower-steering assist control module 135 of the power-steering assistsystem 115 for allowing information to be communicated therebetween. Asteering angle detecting apparatus 140 of the power-steering assistsystem 115 is connected to the power-steering assist control module 135for providing information thereto. The trailer backup assist system isalso attached to a brake system control module 145 and a powertraincontrol module 150 for allowing communication of informationtherebetween. Jointly, the trailer backup assist system 105, thepower-steering assist system 115, the brake system control module 145,the powertrain control module 150, and the gear selection device(PRNDL), define a trailer backup assist architecture configured inaccordance with an embodiment of the inventive subject matter.

The trailer backup assist control module 120 is configured forimplementing logic (i.e., instructions) for receiving information fromthe trailer backup steering input apparatus 125, the hitch angledetecting apparatus 130, the power-steering assist control module 135,the brake system control module 145, and the powertrain control module150. The trailer backup assist control module 120 (e.g., a trailercurvature algorithm thereof) generates vehicle steering information as afunction of all or a portion of the information received from thetrailer backup steering input apparatus 125, the hitch angle detectingapparatus 130, the power-steering assist control module 135, the brakesystem control module 145, and the powertrain control module 150.Thereafter, the vehicle steering information is provided to thepower-steering assist control module 135 for affecting steering of thevehicle 100 by the power-steering assist system 115 to achieve acommanded path of travel for the trailer 110.

The trailer backup steering input apparatus 125 provides the trailerbackup assist control module 120 with information defining the commandedpath of travel of the trailer 110 to the trailer backup assist controlmodule 120 (i.e., trailer steering information). The trailer steeringinformation can include information relating to a commanded change inthe path of travel (e.g., a change in radius of path curvature) andinformation relating to an indication that the trailer is to travelalong a path defined by a longitudinal centerline axis of the trailer(i.e., along a substantially straight path of travel). As will bediscussed below in detail, the trailer backup steering input apparatus125 preferably includes a rotational control input device for allowing adriver of the vehicle 100 to interface with the trailer backup steeringinput apparatus 125 to command desired trailer steering actions (e.g.,commanding a desired change in radius of the path of travel of thetrailer and/or commanding that the trailer travel along a substantiallystraight path of travel as defined by a longitudinal centerline axis ofthe trailer). In a preferred embodiment, the rotational control inputdevice is a knob rotatable about a rotational axis extending through atop surface/face of the knob. In other embodiments, the rotationalcontrol input device is a knob rotatable about a rotational axisextending substantially parallel to a top surface/face of the knob.

Some vehicles (e.g., those with active front steer) have apower-steering assist system configuration that allows a steering wheelto be partially decoupled from movement of the steered wheels of such avehicle. Accordingly, the steering wheel can be rotated independent ofthe manner in which the power-steering assist system of the vehiclecontrols the steered wheels (e.g., as commanded by vehicle steeringinformation provided by a power-steering assist system control modulefrom a trailer backup assist system control module configured inaccordance with an embodiment of the inventive subject matter). As such,in these types of vehicles where the steering wheel can be selectivelydecoupled from the steered wheels to allow independent operationthereof, trailer steering information of a trailer backup assist systemconfigured in accordance with the inventive subject matter can beprovided through rotation of the steering wheel. Accordingly, it isdisclosed herein that in certain embodiments of the inventive subjectmatter, the steering wheel is an embodiment of a rotational controlinput device in the context of the inventive subject matter. In suchembodiments, the steering wheel would be biased (e.g., by an apparatusthat is selectively engagable/activatable) to an at-rest positionbetween opposing rotational ranges of motion.

The hitch angle detecting apparatus 130, which operates in conjunctionwith a hitch angle detection component 155 of the trailer 110, providesthe trailer backup assist control module 120 with information relatingto an angle between the vehicle 100 and the trailer 110 (i.e., hitchangle information). In a preferred embodiment, the hitch angle detectingapparatus 130 is a camera-based apparatus such as, for example, anexisting rear view camera of the vehicle 100 that images (i.e., visuallymonitors) a target (i.e., the hitch angle detection component 155)attached the trailer 110 as the trailer 110 is being backed by thevehicle 100. Preferably, but not necessarily, the hitch angle detectioncomponent 155 is a dedicated component (e.g., an item attachedto/integral with a surface of the trailer 110 for the express purpose ofbeing recognized by the hitch angle detecting apparatus 130.Alternatively, the hitch angle detecting apparatus 130 can be a devicethat is physically mounted on a hitch component of the vehicle 100and/or a mating hitch component of the trailer 110 for determining anangle between centerline longitudinal axes of the vehicle 100 and thetrailer 110. The hitch angle detecting apparatus 130 can be configuredfor detecting a jackknife enabling condition and/or related information(e.g., when a hitch angle threshold has been met).

The power-steering assist control module 135 provides the trailer backupassist control module 120 with information relating to a rotationalposition (e.g., angle) of the steering wheel angle and/or a rotationalposition (e.g., turning angle(s)) of steered wheels of the vehicle 100.In certain embodiments of the inventive subject matter, the trailerbackup assist control module 120 can be an integrated component of thepower steering assist system 115. For example, the power-steering assistcontrol module 135 can include a trailer back-up assist algorithm forgenerating vehicle steering information as a function of all or aportion of information received from the trailer backup steering inputapparatus 125, the hitch angle detecting apparatus 130, thepower-steering assist control module 135, the brake system controlmodule 145, and the powertrain control module 150.

The brake system control module 145 provides the trailer backup assistcontrol module 120 with information relating to vehicle speed. Suchvehicle speed information can be determined from individual wheel speedsas monitored by the brake system control module 145 or may be providedby an engine control module with signal plausibility. Vehicle speed mayalso be determined from an engine control module. In some instances,individual wheel speeds can also be used to determine a vehicle yaw rateand such yaw rate can be provided to the trailer backup assist controlmodule 120 for use in determining the vehicle steering information. Incertain embodiments, the trailer backup assist control module 120 canprovide vehicle braking information to the brake system control module145 for allowing the trailer backup assist control module 120 to controlbraking of the vehicle 100 during backing of the trailer 110. Forexample, using the trailer backup assist control module 120 to regulatespeed of the vehicle 100 during backing of the trailer 110 can reducethe potential for unacceptable trailer backup conditions. Examples ofunacceptable trailer backup conditions include, but are not limited to,a vehicle overspeed condition, a high hitch angle rate, trailer angledynamic instability, a calculated theoretical trailer jackknifecondition (defined by a maximum vehicle steering angle, drawbar length,tow vehicle wheelbase and an effective trailer length), or physicalcontact jackknife limitation (defined by an angular displacement limitrelative to the vehicle 100 and the trailer 110), and the like. It isdisclosed herein that the backup assist control module 120 can issue asignal corresponding to a notification (e.g., a warning) of an actual,impending, and/or anticipated unacceptable trailer backup condition.

The powertrain control module 150 interacts with the trailer backupassist control module 120 for regulating speed and acceleration of thevehicle 100 during backing of the trailer 110. As mentioned above,regulation of the speed of the vehicle 100 is necessary to limit thepotential for unacceptable trailer backup conditions such as, forexample, jackknifing and trailer angle dynamic instability. Similar tohigh-speed considerations as they relate to unacceptable trailer backupconditions, high acceleration and high dynamic driver curvature requestscan also lead to such unacceptable trailer backup conditions.

Steering Input Apparatus

Referring now to FIG. 2, an embodiment of the trailer backup steeringinput apparatus 125 discussed in reference to FIG. 1 is shown. Arotatable control element in the form of a knob 170 is coupled to amovement sensing device 175. The knob 170 is biased (e.g., by a springreturn) to an at-rest position P(AR) between opposing rotational rangesof motion R(R), R(L). A first one of the opposing rotational ranges ofmotion R(R) is substantially equal to a second one of the opposingrotational ranges of motion R(L), R(R). To provide a tactile indicationof an amount of rotation of the knob 170, a force that biases the knob170 toward the at-rest position P(AR) can increase (e.g., non-linearly)as a function of the amount of rotation of the knob 170 with respect tothe at-rest position P(AR). Additionally, the knob 170 can be configuredwith position indicating detents such that the driver can positivelyfeel the at-rest position P(AR) and feel the ends of the opposingrotational ranges of motion R(L), R(R) approaching (e.g., soft endstops).

The movement sensing device 175 is configured for sensing movement ofthe knob 170 and outputting a corresponding signal (i.e., movementsensing device signal) to the trailer assist backup input apparatus 125shown in FIG. 1. The movement sensing device signal is generated as afunction of an amount of rotation of the knob 170 with respect to theat-rest position P(AR), a rate movement of the knob 170, and/or adirection of movement of the knob 170 with respect to the at-restposition P(AR). As will be discussed below in greater detail, theat-rest position P(AR) of the knob 170 corresponds to a movement sensingdevice signal indicating that the vehicle 100 should be steered suchthat the trailer 100 is backed along a substantially straight path (zerotrailer curvature request from the driver) as defined by a centerlinelongitudinal axis of the trailer 110 when the knob 170 was returned tothe at-rest position P(AR) and a maximum clockwise and anti-clockwiseposition of the knob 170 (i.e., limits of the opposing rotational rangesof motion R(R), R(L)) each correspond to a respective movement sensingdevice signal indicating a tightest radius of curvature (i.e., mostacute trajectory) of a path of travel of the trailer 110 that ispossible without the corresponding vehicle steering information causinga jackknife condition. In this regard, the at-rest position P(AR) is azero curvature commanding position with respect to the opposingrotational ranges of motion R(R), R(L). It is disclosed herein that aratio of a commanded curvature of a path of a trailer (e.g., radius of atrailer trajectory) and a corresponding amount of rotation of the knobcan vary (e.g., non-linearly) over each one of the opposing rotationalranges of motion P(L), P(R) of the knob 170. It is also disclosedtherein that the ratio can be a function of vehicle speed, trailergeometry, vehicle geometry, hitch geometry and/or trailer load.

Use of the knob 170 decouples trailer steering inputs from being made ata steering wheel of the vehicle 100. In use, as a driver of the vehicle100 backs the trailer 110, the driver can turn the knob 170 to indicatea desired curvature of a path of the trailer 110 to follow and returnsthe knob 170 to the at-rest position P(AR) for causing the trailer 110to be backed along a straight line. Accordingly, in embodiments oftrailer backup assist systems where the steering wheel remainsphysically coupled to the steerable wheels of a vehicle during backup ofan attached trailer, a rotatable control element configured inaccordance with the inventive subject matter (e.g., the knob 170)provides a simple and user-friendly means of allowing a driver of avehicle to input trailer steering commands.

It is disclosed herein that a rotational control input device configuredin accordance with embodiments of the inventive subject matter (e.g.,the knob 170 and associated movement sensing device) can omit a meansfor being biased to an at-rest position between opposing rotationalranges of motion. Lack of such biasing allows a current rotationalposition of the rotational control input device to be maintained untilthe rotational control input device is manually moved to a differentposition. Preferably, but not necessarily, when such biasing is omitted,a means is provided for indicating that the rotational control inputdevice is positioned in a zero curvature commanding position (e.g., atthe same position as the at-rest position in embodiments where therotational control input device is biased). Examples of means forindicating that the rotational control input device is positioned in thezero curvature commanding position include, but are not limited to, adetent that the rotational control input device engages when in the zerocurvature commanding position, a visual marking indicating that therotational control input device is in the zero curvature commandingposition, an active vibratory signal indicating that the rotationalcontrol input device is in or approaching the zero curvature commandingposition, an audible message indicating that the rotational controlinput device is in of approaching the zero curvature commandingposition, and the like.

It is also disclosed herein that embodiments of the inventive subjectmatter can be configured with a control input device that is notrotational (i.e., a non-rotational control input device). Similar to arotational control input device configured in accordance withembodiments of the inventive subject matter (e.g., the knob 170 andassociated movement sensing device), such a non-rotational control inputdevice is configured to selectively provide a signal causing a trailerto follow a path of travel segment that is substantially straight and toselectively provide a signal causing the trailer to follow a path oftravel segment that is substantially curved. Examples of such anon-rotational control input device include, but are not limited to, aplurality of depressible buttons (e.g., curve left, curve right, andtravel straight), a touch screen on which a driver traces or otherwiseinputs a curvature for path of travel commands, a button that istranslatable along an axis for allowing a driver to input path of travelcommands, or joystick type input and the like.

The trailer backup steering input apparatus 125 can be configured toprovide various feedback information to a driver of the vehicle 100.Examples of situation that such feedback information can include, butare not limited to, a status of the trailer backup assist system 105(e.g., active, in standby (e.g., when driving forward to reduce thetrailer angle and zero trailer angle to remove bias), faulted, inactive,etc.), that a curvature limit has been reached (i.e., maximum commandedcurvature of a path of travel of the trailer 110), and/or a graphicalrepresentation of the vehicle and trailer orientation state. To thisend, the trailer backup steering input apparatus 125 can be configuredto provide a tactile feedback signal (e.g., a vibration through the knob170) as a warning if any one of a variety of conditions occur. Examplesof such conditions include, but are not limited to, the trailer 110approaching jackknife, the trailer backup assist system 105 has had afailure, the trailer backup assist system 105 has detected a fault, thetrailer backup assist system 105 or other system of the vehicle 100 haspredicted a collision on the present path of travel of the trailer 110,the trailer backup system 105 has restricted a commanded curvature of atrailer's path of travel (e.g., due to excessive speed or accelerationof the vehicle 100), and the like. Still further, it is disclosed thatthe trailer backup steering input apparatus 125 can use illumination(e.g. an LED 180) and/or an audible signal output (e.g., an audibleoutput device 185 or through attached vehicle audio speakers) to providecertain feedback information (e.g., notification/warning of anunacceptable trailer backup condition).

Referring now to FIGS. 2 and 3, an example of using the trailer backupsteering input apparatus 125 for dictating a curvature of a path oftravel (POT) of a trailer (i.e., the trailer 110 shown in FIG. 1) whilebacking up the trailer with a vehicle (i.e., the vehicle 100 in FIGS. 1and 2) is shown. In preparation of backing the trailer 110, the driverof the vehicle 100 drives the vehicle 100 forward along a pull-thru path(FTP) to position the vehicle 100 and trailer 110 at a first backupposition B1. In the first backup position B1, the vehicle 100 andtrailer 110 are longitudinally aligned with each other such that alongitudinal centerline axis L1 of the vehicle 100 is aligned with(e.g., parallel with or coincidental with) a longitudinal centerlineaxis L2 of the trailer 110. It is disclosed herein that such alignmentof the longitudinal axes L1, L2 at the onset of an instance of trailerbackup functionality is not a requirement for operability of a trailerbackup assist system configured in accordance with the inventive subjectmatter.

After activating the trailer backup assist system 105 (e.g., before,after, or during the pull-thru sequence), the driver begins to back thetrailer 110 by reversing the vehicle 100 from the first backup positionB1. So long as the knob 170 of the trailer backup steering inputapparatus 125 remains in the at-rest position P(AR), the trailer backupassist system 105 will steer the vehicle 100 as necessary for causingthe trailer 110 to be backed along a substantially straight path oftravel as defined by the longitudinal centerline axis L2 of the trailer110 at the time when backing of the trailer 110 began. When the trailerreaches the second backup position B2, the driver rotates the knob 170to command the trailer 110 to be steered to the right (i.e., a knobposition R(R) clockwise rotation). Accordingly, the trailer backupassist system 105 will steer the vehicle 100 for causing the trailer 110to be steered to the right as a function of an amount of rotation of theknob 170 with respect to the at-rest position P(AR), a rate movement ofthe knob 170, and/or a direction of movement of the knob 170 withrespect to the at-rest position P(AR). Similarly, the trailer 110 can becommanded to steer to the left by rotating the knob 170 to the left.When the trailer reaches backup position B3, the driver allows the knob170 to return to the at-rest position P(AR) thereby causing the trailerbackup assist system 105 to steer the vehicle 100 as necessary forcausing the trailer 110 to be backed along a substantially straight pathof travel as defined by the longitudinal centerline axis L2 of thetrailer 110 at the time when the knob 170 was returned to the at-restposition P(AR). Thereafter, the trailer backup assist system 105 steersthe vehicle 100 as necessary for causing the trailer 110 to be backedalong this substantially straight path to the fourth backup position B4.In this regard, arcuate portions of a path of travel POT of the trailer110 are dictated by rotation of the knob 170 and straight portions ofthe path of travel POT are dictated by an orientation of the centerlinelongitudinal axis L2 of the trailer when the knob 170 is in/returned tothe at-rest position P(AR).

In order to activate the trailer backup assist system described above inFIGS. 1 through 3, the driver interacts with the trailer backup assistsystem and the trailer backup assist system interacts with the vehicleenvironment. The trailer backup assist system automatically steers asthe driver reverses the vehicle. As discussed above, the driver controlsthe trailer trajectory by using a steering knob to input desired trailercurvature. The trailer backup assist algorithm determines the vehiclesteering angle to achieve the desired trailer curvature, and the drivercontrols the throttle and brake while the trailer backup assist systemcontrols the steering.

FIG. 4 shows a method 200 for implementing trailer backup assistfunctionality in accordance with an embodiment of the inventive subjectmatter. In a preferred embodiment, the method 200 for implementingtrailer backup assist functionality can be carried out using the trailerbackup assist architecture discussed above in reference to the vehicle100 and trailer 110 of FIG. 1. Accordingly, trailer steering informationis provided through use of a rotational control input device (e.g., theknob 170 discussed in reference to FIG. 2).

An operation 202 is performed for receiving a trailer backup assistrequest. Examples of receiving the trailer backup assist request includeactivating the trailer backup assist system and providing confirmationthat the vehicle and trailer are ready to be backed. After receiving atrailer backup assist request (i.e., while the vehicle is beingreversed), an operation 204 is performed for receiving a trailer backupinformation signal. Examples of information carried by the trailerbackup information signal include, but are not limited to, informationfrom the trailer backup steering input apparatus 125, information fromthe hitch angle detecting apparatus 130, information from thepower-steering assist control module 135, information from the brakesystem control module 145, and information from the powertrain controlmodule 150. It is disclosed herein that information from the trailerbackup steering input apparatus 125 preferably includes trailer pathcurvature information characterizing a desired curvature for the path oftravel of the trailer, such as provided by the trailer backup steeringinput apparatus 125 discussed above in reference to FIGS. 1 and 2. Inthis manner, the operation 204 for receiving the trailer backupinformation signal can include receiving trailer path curvatureinformation characterizing the desired curvature for the path of travelof the trailer.

If the trailer backup information signal indicates that a change incurvature of the trailer's path of travel is requested (i.e., commandedvia the knob 170), an operation 206 is performed for determining vehiclesteering information for providing the requested change in curvature ofthe trailer's path of travel. Otherwise, an operation 208 is performedfor determining vehicle steering information for maintaining a currentstraight-line heading of the trailer (i.e., as defined by thelongitudinal centerline axis of the trailer). Thereafter, an operation210 is performed for providing the vehicle steering information to apower-steering assist system of the vehicle, followed by an operation212 being performed for determining the trailer backup assist status. Ifit is determined that trailer backup is complete, an operation 214 isperformed for ending the current trailer backup assist instance.Otherwise the method 200 returns to the operation 204 for receivingtrailer backup information. Preferably, the operation for receiving thetrailer backup information signal, determining the vehicle steeringinformation, providing the vehicle steering information, and determiningthe trailer backup assist status are performed in a monitoring fashion(e.g., at a high rate of speed of a digital data processing device).Accordingly, unless it is determined that reversing of the vehicle forbacking the trailer is completed (e.g., due to the vehicle having beensuccessfully backed to a desired location during a trailer backup assistinstance, the vehicle having to be pulled forward to begin anothertrailer backup assist instance, etc.), the method 200 will continuallybe performing the operations for receiving the trailer backupinformation signal, determining the vehicle steering information,providing the vehicle steering information, and determining the trailerbackup assist status.

It is disclosed herein that the operation 206 for determining vehiclesteering information for providing the requested change in curvature ofthe trailer's path of travel preferably includes determining vehiclesteering information as a function of trailer path curvature informationcontained within the trailer backup information signal. As will bediscussed below in greater detail, determining vehicle steeringinformation can be accomplished through a low order kinematic modeldefined by the vehicle and the trailer. Through such a model, arelationship between the trailer path curvature and commanded steeringangles of steered wheels of the vehicle can be generated for determiningsteering angle changes of the steered wheels for achieving a specifiedtrailer path curvature. In this manner, the operation 206 fordetermining vehicle steering information can be configured forgenerating information necessary for providing trailer path curvaturecontrol in accordance with the inventive subject matter.

In some embodiments of the inventive subject matter, the operation 210for providing the vehicle steering information to the power-steeringassist system of the vehicle causes the steering system to generate acorresponding steering command as a function of the vehicle steeringinformation. The steering command is interpretable by the steeringsystem and is configured for causing the steering system to move steeredwheels of the steering system for achieving a steered angle as specifiedby the vehicle steering information. Alternatively, the steering commandcan be generated by a controller, module or computer external to thesteering system (e.g., a trailer backup assist control module) and beprovided to the steering system.

In parallel with performing the operations for receiving the trailerbackup information signal, determining the vehicle steering information,providing the vehicle steering information, and determining the trailerbackup assist status, the method 200 performs an operation 216 formonitoring the trailer backup information for determining if anunacceptable trailer backup condition exists. Examples of suchmonitoring include, but are not limited to assessing a hitch angle todetermine if a hitch angle threshold is exceeded, assessing a backupspeed to determine if a backup speed threshold is exceeded, assessingvehicle steering angle to determine if a vehicle steering anglethreshold is exceeded, assessing other operating parameters (e.g.,vehicle longitudinal acceleration, throttle pedal demand rate and hitchangle rate) for determining if a respective threshold value is exceeded,and the like. Backup speed can be determined from wheel speedinformation obtained from one or more wheel speed sensors of thevehicle. If it is determined that an unacceptable trailer backupcondition exists, an operation 218 is performed for causing the currentpath of travel of the trailer to be inhibited (e.g., stopping motion ofthe vehicle), followed by the operation 214 being performed for endingthe current trailer backup assist instance. It is disclosed herein thatprior to and/or in conjunction with causing the current trailer path tobe inhibited, one or more actions (e.g., operations) can be implementedfor providing the driver with feedback (e.g., a warning) that such anunacceptable trailer angle condition is impending or approaching. In oneexample, if such feedback results in the unacceptable trailer anglecondition being remedied prior to achieving a critical condition, themethod can continue with providing trailer backup assist functionalityin accordance with operations 204-212. Otherwise, the method can proceedto operation 214 for ending the current trailer backup assist instance.In conjunction with performing the operation 214 for ending the currenttrailer backup assist instance, an operation can be performed forcontrolling movement of the vehicle to correct or limit a jackknifecondition (e.g., steering the vehicle, decelerating the vehicle,limiting magnitude and/or rate of driver requested trailer curvatureinput, limiting magnitude and/or rate of the steering command, and/orthe like to preclude the hitch angle from being exceeded).

Curvature Control Algorithm

Turning now to a discussion of a kinematic model used to calculate arelationship between a curvature of a path of travel of a trailer andthe steering angle of a vehicle towing the trailer, a low orderkinematic model can be desirable for a trailer back-up assist systemconfigured in accordance with some embodiments of the inventive subjectmatter. To achieve such a low order kinematic model, certain assumptionsare made with regard to parameters associated with the vehicle/trailersystem. Examples of such assumptions include, but are not limited to,the trailer being backed by the vehicle at a relatively low speed,wheels of the vehicle and the trailer having negligible (e.g., no) slip,tires of the vehicle having negligible (e.g., no) lateral compliance,tires of the vehicle and the trailer having negligible (e.g., no)deformation, actuator dynamics of the vehicle being negligible, thevehicle and the trailer exhibiting negligible (e.g., no) roll or pitchmotions.

As shown in FIG. 5, for a system defined by a vehicle 302 and a trailer304, the kinematic model 300 is based on various parameters associatedwith the vehicle 302 and the trailer 304. These kinematic modelparameters include:

δ: steering angle at steered front wheels 306 of the vehicle 302;

α: yaw angle of the vehicle 302;

β: yaw angle of the trailer 304;

γ: hitch angle (γ=(β−α);

W: wheel base of the vehicle 302;

L: length between hitch point 308 and rear axle 310 of the vehicle 302;

D: length between hitch point 308 and axle length 312 of the trailer 304(axle length 312 may be an effective, or equivalent, axle length for atrailer having a multiple axle configuration; and

r₂: curvature radius for the trailer 304.

The kinematic model 300 of FIG. 5 reveals a relationship between trailerpath radius of curvature r₂ at the midpoint 314 of an axle 312 of thetrailer 304, steering angle δ of the steered wheels 306 of the vehicle302, and the hitch angle γ. As shown in the equation below, thisrelationship can be expressed to provide the trailer path curvature κ2such that, if γ is given, the trailer path curvature κ2 can becontrolled based on regulating the steering angle δ (where {dot over(β)} is trailer yaw rate and {dot over (η)} is trailer velocity).

$\kappa_{2} = {\frac{1}{r_{2}} = {\frac{\overset{*}{\beta}}{\overset{*}{\eta}} = \frac{{( {W + \frac{K\; V^{2}}{g}} )\sin\;\gamma}\; + {L\;\cos\;{\gamma tan}\;\delta}}{D( {{( {W + \frac{K\; V^{2}}{g}} )\cos\;\gamma}\; - {L\;\sin\;{\gamma tan}\;\delta}} )}}}$

Or, this relationship can be expressed to provide the steering angle δas a function of trailer path curvature κ2 and hitch angle γ.

$\delta = {{\tan^{- 1}( \frac{( {W + \frac{K\; V^{2}}{g}} )\lbrack {{\kappa_{2}D\;\cos\;\gamma}\; - {\sin\;\gamma}} \rbrack}{{{DL}\;\kappa_{2}\sin\;\gamma}\; + {L\;\cos\;\gamma}} )} = {F( {\gamma,\kappa_{2},K} )}}$

Accordingly, for a particular vehicle and trailer combination, certainkinematic model parameters (e.g., D, W and L) are constant and assumedknown. V is the vehicle longitudinal speed and g is the acceleration dueto gravity. K is a speed dependent parameter which when set to zeromakes the calculation of steering angle independent of vehicle speed.For example, vehicle-specific kinematic model parameters can bepredefined in an electronic control system of a vehicle andtrailer-specific kinematic model parameters can be inputted by a driverof the vehicle. Trailer path curvature κ₂ is determined from the driverinput via a trailer backup steering input apparatus. Through the use ofthe equation for providing steering angle, a corresponding steeringcommand can be generated for controlling a steering system (e.g., anactuator thereof) of the vehicle.

FIG. 6 shown an example of a trailer path curvature function plot 400for a rotary-type trailer backup steering input apparatus (e.g., thetrailer backup steering input apparatus 125 discussed above in referenceto FIGS. 1 and 2). A value representing trailer path curvature (e.g.,trailer path curvature κ2) is provided as an output signal from therotary-type trailer backup steering input apparatus as a function ofuser input movement. In this example, a curve 402 specifying trailerpath curvature relative to user input (e.g., amount of rotation) at arotary input device (e.g. a knob) is defined by a cubic function.However, a skilled person will appreciate that embodiments of theinventive subject matter are not limited to any particular functionbetween a magnitude and/or rate of input at a trailer backup steeringinput apparatus (e.g., knob rotation) and a resulting trailer pathcurvature value.

Jackknife Detection

Referring to FIG. 5, in preferred embodiments of the inventive subjectmatter, it is desirable to limit the potential for the vehicle 302 andthe trailer 304 to attain a jackknife angle (i.e., the vehicle/trailersystem achieving a jackknife condition). A jackknife angle γ (j) refersto a hitch angle γ that while backing cannot be overcome by the maximumsteering input for a vehicle such as, for example, the steered frontwheels 306 of the vehicle 302 being moved to a maximum steered angle δat a maximum rate of steering angle change. The jackknife angle γ(j) isa function of a maximum wheel angle for the steered wheel 306 of thevehicle 302, the wheel base W of the vehicle 302, the distance L betweenhitch point 308 and the rear axle 310 of the vehicle 302, and the lengthD between the hitch point 308 and the effective axle 312 of the trailer304 when the trailer has multiple axles. The effective axle 312 may bethe actual axle for a single axle trailer or an effective axle locationfor a trailer with multiple axles. When the hitch angle γ for thevehicle 302 and the trailer 304 achieves or exceeds the jackknife angleγ(j), the vehicle 302 must be pulled forward to reduce the hitch angleγ. Thus, for limiting the potential for a vehicle/trailer systemattaining a jackknife angle, it is preferable to control the yaw angleof the trailer while keeping the hitch angle of the vehicle/trailersystem relatively small.

Referring to FIGS. 5 and 7, a steering angle limit for the steered frontwheels 306 requires that the hitch angle γ cannot exceed the jackknifeangle γ (j), which is also referred to as a critical hitch angle. Thus,under the limitation that the hitch angle γ cannot exceed the jackknifeangle γ(j), the jackknife angle γ (j) is the hitch angle γ thatmaintains a circular motion for the vehicle/trailer system when thesteered wheels 306 are at a maximum steering angle δ(max). The steeringangle for circular motion with hitch angle is defined by the followingequation.

${\tan\;\delta_{\max}} = \frac{W\;\sin\;\gamma_{\max}}{D + {L\;\cos\;\gamma_{\max}}}$

Solving the above equation for hitch angle allows jackknife angle γ(j)to be determined. This solution, which is shown in the followingequation, can be used in implementing trailer backup assistfunctionality in accordance with the inventive subject matter formonitoring hitch angle in relation to jackknife angle.

${\cos\;\overset{\_}{\gamma}} = \frac{{- b} \pm \sqrt{b^{2} - {4\; a\; c}}}{2\; a}$

where,a=L ² tan²δ(max)+W ²;b=2LD tan²δ(max); andc=D ² tan²δ(max)−W ².

In certain instances of backing a trailer, a jackknife enablingcondition can arise based on current operating parameters of a vehiclein combination with a corresponding hitch angle. This condition can beindicated when one or more specified vehicle operating thresholds aremet while a particular hitch angle is present. For example, although theparticular hitch angle is not currently at the jackknife angle for thevehicle and attached trailer, certain vehicle operating parameters canlead to a rapid (e.g., uncontrolled) transition of the hitch angle tothe jackknife angle for a current commanded trailer path curvatureand/or can reduce an ability to steer the trailer away from thejackknife angle. One reason for a jackknife enabling condition is thattrailer curvature control mechanisms (e.g., those in accordance with theinventive subject matter) generally calculate steering commands at aninstantaneous point in time during backing of a trailer. However, thesecalculations will typically not account for lag in the steering controlsystem of the vehicle (e.g., lag in a steering EPAS controller). Anotherreason for the jackknife enabling condition is that trailer curvaturecontrol mechanisms generally exhibit reduced steering sensitivity and/oreffectiveness when the vehicle is at relatively high speeds and/or whenundergoing relatively high acceleration.

Jackknife Counter-Measures

FIG. 8 shows a method 500 for implementing jackknife countermeasuresfunctionality in accordance with an embodiment of the inventive subjectmatter for a vehicle and attached trailer. Trailer backup assistfunctionality in accordance with the inventive subject matter caninclude jackknife countermeasures functionality. Alternatively,jackknife countermeasures functionality in accordance with an embodimentof the inventive subject matter can be implemented separately from otheraspects of trailer backup assist functionality.

The method 500 begins when operation 502 is performed for receivingjackknife determining information characterizing a jackknife enablingcondition of the vehicle-trailer combination at a particular point intime (e.g., at the point in time when the jackknife determininginformation was sampled). Examples of the jackknife determininginformation includes, but are not limited to, information characterizinga hitch angle, information characterizing a vehicle accelerator pedaltransient state, information characterizing a speed of the vehicle,information characterizing longitudinal acceleration of the vehicle,information characterizing a brake torque being applied by a brakesystem of the vehicle, information characterizing a powertrain torquebeing applied to driven wheels of the vehicle, and informationcharacterizing the magnitude and rate of driver requested trailercurvature. The operation 502 for receiving jackknife determininginformation can be the first operation in a sampling process wherejackknife determining information is sampled upon initiation of aninstance of implementing jackknife countermeasures functionality. Inthis regard, jackknife determining information would be continuallymonitored such as, for example, by an electronic control unit (ECU) thatcarries out trailer backup assist (TBA) functionality. As discussedabove in reference to FIG. 5, a kinematic model representation of thevehicle and the trailer can be used to determine a jackknife angle forthe vehicle-trailer combination. However, the inventive subject matteris not unnecessarily limited to any specific approach for determiningthe jackknife angle.

After receiving the jackknife determining information, an operation 504is performed for assessing the jackknife determining information fordetermining if the vehicle-trailer combination attained the jackknifeenabling condition at the particular point in time. The objective of theoperation 504 for assessing the jackknife determining information isdetermining if a jackknife enabling condition has been attained at thepoint in time defined by the jackknife determining information. If it isdetermined that a jackknife enabling condition is not present at theparticular point in time, the method 500 returns to the operation 502for receiving another instance of the jackknife determining information.If it is determined that a jackknife enabling condition is present atthe particular point in time, an operation 506 is performed fordetermining an applicable counter-measure or counter-measures toimplement. Accordingly, in some embodiments of the inventive subjectmatter, an applicable counter-measure will be selected dependent upon aparameter identified as being a key influencer of the jackknife enablingcondition. However, in other embodiments, an applicable counter-measurewill be selected as being most able to readily alleviate the jackknifeenabling condition. In still other embodiment, a pre-definedcounter-measure or pre-defined set of counter-measures may be theapplicable counter-measure(s).

The objective of a counter-measure in the context of the inventivesubject matter (i.e., a jackknife reduction countermeasure) is toalleviate a jackknife enabling condition. To this end, such acounter-measure can be configured to alleviate the jackknife enablingcondition using a variety of different strategies. In a vehicle speedsensitive counter-measure strategy, actions taken for alleviating thejackknife enabling condition can include overriding and/or limitingdriver requested trailer radius of curvature (e.g., being requested viaa trailer backup steering input apparatus configured in accordance withthe inventive subject matter) as a function of vehicle speed (e.g., viaa look-up table correlating radius of curvature limits to vehicle speedas shown in FIG. 6). In a counter-measure strategy where trailercurvature requests are limited as a function of speed and drivercurvature command transient rates, actions taken for alleviating thejackknife enabling condition can include rate limiting trailer curvaturecommand transients as requested by a driver above a pre-defined vehiclespeed whereas, under the pre-defined vehicle speed, the as-requestedtrailer curvature are not rate limited. In a torque limitingcounter-measure strategy, actions taken for alleviating the jackknifeenabling condition can include application of full available powertraintorque being inhibited when the jackknife enabling condition is presentwhile the vehicle is above a pre-defined speed and application of fullavailable powertrain torque being allowed when the vehicle speed isreduced below the pre-defined speed while in the torque inhibiting mode.As opposed to a fixed pre-defined speed, the torque limitingcounter-measure strategy can utilize a speed threshold that is afunction of hitch angle (i.e., speed threshold inversely proportional tohitch angle acuteness). In a driver accelerator pedal transientdetection counter-measure strategy, actions taken for alleviating thejackknife enabling condition can include overriding and/or limitingdriver requested trailer radius of curvature as a function of transientaccelerator pedal requests (e.g., requested trailer radius of curvaturelimited when a large accelerator pedal transient is detected). In ahitch angle rate sensitive counter-measure strategy, actions taken foralleviating the jackknife enabling condition can include using hitchangle rate in a predefined or calculated mapping with current hitchangle position to limit driver requested trailer radius of curvature.Accordingly, in view of the disclosures made herein, a skilled personwill appreciate that embodiments of the inventive subject matter are notunnecessarily limited to a counter-measure strategy of any particularconfiguration.

As disclosed above, implementation of trailer backup assistfunctionality in accordance with the inventive subject matter canutilize a kinematic model for determining steering control information,jackknife enabling conditions, and jackknife angle. Such a kinematicmodel has many parameters than can influence trailer curvature controleffectiveness. Examples of these parameters include, but are not limitedto, the vehicle wheelbase, understeer gradient gain, vehicle trackwidth, maximum steer angle at the vehicle front wheels, minimum turningradius of vehicle, maximum steering rate able to be commanded by thesteering system, hitch ball to trailer axle length, and vehicle rearaxle to hitch ball length. Sensitivity analysis for a given kinematicmodel can be used to provide an understanding (e.g., sensitivity) of therelationships between such parameters, thereby providing informationnecessary for improving curvature control performance and for reducingthe potential for jackknife enabling conditions. For example, through anunderstanding of the sensitivity of the parameters of a kinematic model,scaling factors can be used with speed dependent jackknifecounter-measures to reduce jackknife potential (e.g., for specialapplications such as short wheelbase conditions).

Still referring to FIG. 8, after determining the applicablecountermeasure(s), an operation 508 is performed for implementing thechosen jackknife countermeasure(s) and an operation 510 is performed forinitiating a jackknife warning. As discussed above in regard tocounter-measure strategies, implementing the jackknifecounter-measure(s) can include commanding a speed controlling system ofthe vehicle to transition to an altered state of operation in which aspeed of the vehicle is reduced, commanding the steering control systemof the vehicle to transition to an altered state of operation in which aradius of curvature of a path of the trailer is increased, command thesteering control system of the vehicle to transition to an altered stateof operation in which a decrease in the radius of the curvature of thepath of the trailer is inhibited, commanding a brake control system ofthe vehicle to apply brake torque to reduce vehicle speed/inhibitvehicle acceleration, and/or commanding a powertrain control system ofthe vehicle to inhibit full available powertrain torque from beingdelivered to driven wheels of the vehicle until another jackknifeenabling parameter (e.g., vehicle speed) is below a defined threshold.In certain embodiments of the inventive subject matter, the jackknifewarning is provided to the driver using at least one vehicle controlsystem through which the jackknife counter-measure is implemented. Speedreduction, in addition to applying the brakes, can be accomplished byany number of means such as, for example, limiting throttle inputs(e.g., via a terrain management feature) and/or transitioning atransmission to a reverse low gear if the vehicle is equipped with amulti-range reverse gear transmission. Examples of such system-specificwarning approach include, but are not limited to, providing a warningthrough an accelerator pedal of the vehicle (e.g., via haptic feedback)if the counter-measure includes limiting speed of the vehicle and/orproviding a warning through an input element (e.g., knob) of a trailerbackup steering input apparatus of the vehicle (e.g., via hapticfeedback if the counter-measure includes limiting driver requestedtrailer radius of curvature), through haptic seat vibration warning,through a visual warning (e.g., through a visual display apparatus ofthe towing vehicle) and/or through audible warnings (e.g., through anaudio output apparatus of the towing vehicle), or the like. Oneembodiment of utilizing warnings relating to vehicle speed as it relatesto onset or presence of a jackknife enabling condition includesimplementation of a dual stage warning. For example, when a backingspeed of the vehicle increases sufficiently for causing a speed of thevehicle to reach a lower (i.e., first) speed threshold during backing ofthe trailer, a driver of the vehicle would be provided with a firstwarning indication (e.g., via haptic, audible, and/or visual means asimplemented by the trailer backup assist system) for informing thedriver that there is the need to reduce the speed of the vehicle toalleviate or preclude the jackknife enabling condition. If the driverdoes not correspondingly respond by causing a speed of the vehicle to bereduced (or not to further increase) and the vehicle continues to gainspeed such that it passes a higher (i.e., a second) speed threshold, thedriver of the vehicle would be provided with a second warning indication(e.g., a more severe haptic, audible, and/or visual means as implementedby the trailer backup assist system) for informing the driver that thereis an immediate need to reduce the speed of the vehicle to alleviate orpreclude the jackknife enabling condition. The first and/or the secondspeed indication warnings can be implemented in conjunction with arespective speed limiting counter-measure or measures (e.g., the trailerbackup assist system causing activation of a brake system of the vehicleand/or reducing a throttle position of the vehicle).

Human Machine Interface

In order to implement the control features discussed above with respectto methods described in FIG. 5 and FIG. 8, a driver must interact withthe trailer backup assist system 105 to configure the system 105. Thevehicle 100 is also equipped, as shown in FIG. 9, with a Human MachineInterface (HMI) device 102 to implement trailer backup assistfunctionality through driver interaction with the HMI device 102.

FIG. 9 shows an example of an HMI device 102 in the vehicle that adriver uses to interact with the trailer backup assist system 105. Thedriver is presented with multiple menus 104 (only one example menu isshown in FIG. 9) displayed by way of the HMI 102. The HMI menus 104assist the driver through modules (shown in FIGS. 10 and 11) that setup600, calibrate 700, and activate 800 the trailer back-up assist system105 so that control methods 200, 500 may be implemented to assist thedriver with the backup of the trailer shown generally as a flow diagramin FIGS. 10 and 11, and to be discussed in greater detail later herein.Each module is directed to particular elements, or features, which areused to configure the trailer backup assist system to accuratelyimplement control methods 200, 500. While each module is described withreference to particular features of the inventive subject matter, itshould be noted that each module is not necessarily limited to theparticular features described in the examples herein. It is possible torearrange the modules or to replace elements or features of a modulewithout departing from the scope of the inventive subject matter.

The trailer backup assist system 105 will guide a driver through thesteps necessary to connect a trailer and attach a target. The driver mayactivate the setup by way of the backup steering input apparatus 125,for example by turning or pushing the rotary knob, or my merely making aselection for the Trailer Backup Assist System from a menu on the HMIdevice 102. Referring to FIG. 10, a driver initiates the trailer backupassist system through the trailer backup assist steering inputapparatus. In the case of a rotary knob, the driver presses or rotatesthe knob to initiate the trailer backup assist system. The system willguide the driver through the steps of connecting 580 a compatibletrailer 110. A compatible trailer is one that pivots at a single pointrelative to the vehicle and behind the rear axle of the vehicle.

Once the system is selected by either the trailer backup steering inputapparatus 125 or the HMI device 105, the system will guide the driver toprepare the vehicle and vehicle trailer combination as necessary. Thevehicle 100 should be turned “on” and the vehicle 100 should be in“park” 590. In the event the vehicle 100 is on but is traveling at aspeed that is greater than a predetermined limit, for example five milesper hour, the trailer backup assist system 105 will become inactive andinaccessible to the driver. The trailer backup assist system 105 setupmodule 600 will not begin or will be exited 585. If the type of trailer110 selected by the driver is a trailer 110 that is not compatible withthe trailer backup assist system 105, the setup module 600 will beexited 585 or will not begin. In the event, the trailer 110 iscompatible with the trailer backup assist system 105, the setup module600 verifies that the vehicle 100 gear shift mechanism is in “park”.Again, in the event the vehicle is not “on” and the gear shift mechanismis not on “park”, the setup module will not begin 585.

Upon connection 580 of a compatible trailer 110, the vehicle 100 being“on” 590 and the vehicle 100 being in “park” 590, the HMI 102 willpresent a menu 104 that has a “Towing” mode option to be selected by thedriver. The driver selects “Towing” mode and a menu 104 is presentedthat provides a “Trailer Options” selection. The driver then selects a“Trailer Options” mode from the “Towing” menu. The driver is prompted toeither “add a trailer” or “select a trailer” from a menu 104 presentedon the HMI device and the “Setup” module 600 of the inventive subjectmatter has begun. For certain camera-based trailer angle detectionsystems, an operation 602 is performed wherein a warning menu may bepresented to the driver, by way of the HMI, informing the driver thatthe trailer must be in a straight line, meaning there is no angle at thehitch between the vehicle and the trailer. The warning indicates thatthe driver may need to take corrective action, for example, pull thevehicle forward in order to align the trailer and the vehicle asrequired for the setup 600. A generic or static graphic may be presentedby way of the HMI 102 to assist the driver in visually recognizing thealignment between the trailer 110 and the vehicle 100 that is necessaryin order to properly setup and calibrate the trailer backup assistsystem 105. The driver applies any corrections 603 in that the drivermakes any necessary adjustment he has been alerted to and indicates, byacknowledging that corrective actions have been applied 603 and that thetrailer is in line with the vehicle. Other trailer angle detectionsystems may not need the driver to straighten the trailer during setupmode.

To aid the driver in the setup process, the reverse back lights, or anyother supplemental lighting that may be available on the vehicle, areilluminated 604. In the event the trailer is a new trailer, one thathasn't been attached to the vehicle before or hasn't been previouslystored in the trailer backup assist system, the driver is presented 606with an option to either name the trailer or select a previously storedtrailer configuration. Naming the trailer 608 allows the trailer to beeasily identified the next time it is attached to the vehicle so thatthe driver doesn't have to repeat the setup process. The driver eitherenters a unique name to identify the trailer that is to be stored in thetrailer backup assist system or selects a previously stored trailerconfiguration associated with the attached trailer. The trailer backupassist system will not allow more than one trailer to have the samename. Therefore, if a driver attempts to name a trailer using a namethat has already been applied to a previously stored trailerconfiguration, the HMI will display a message to the driver indicatingso and requesting the driver enter a different name for the trailerconfiguration. In the case where a previously stored trailerconfiguration is available and selected 610 by the driver, certain stepsin the setup process may be skipped.

The following discussion is directed to a first time trailerconfiguration for a camera-based trailer angle detection system. Thedriver is instructed 612 to place a hitch angle target on the trailerthat is used for calibration purposes. A generic static image may bedisplayed on the HMI that provides direction to the driver as toplacement of a target on the trailer that is used for hitch angledetection. The target placement is dependent upon the type of trailerbeing towed and therefore, options may be presented to the driver to aidthe driver in selecting an appropriate trailer type. The static imagemay indicate areas that are acceptable for target placement as well asareas that are unacceptable for target placement. The static imageindicating the appropriate areas for attaching the target may be anoverlay of the rear view of the trailer hitch. Once the driver attachesthe target to the trailer and indicates by way of the HMI that thetarget has been attached to the trailer the setup mode provides 614visual feedback to the driver identifying that the target has beenlocated, or acquired. The driver acknowledges 616, by way of the HMI,that the target has been properly identified by the trailer backupassist system. Similarly, for a previously stored trailer configuration,the trailer will already have a target placed thereon. The trailerbackup assist system will acquire the target and provide 614 visualfeedback to the driver confirming acquisition of the target.

In the event the target is not acquired 614 after a predetermined amountof time lapses, the driver is notified 618 of the need to reposition thetarget and presented with possible corrective measures that may betaken. Possible corrective measures may be presented to the driver suchas cleaning the camera lens, cleaning the target, replacing the targetif it has been damaged or faded, pulling the vehicle-trailer combinationforward to improve lighting conditions around the camera and/or target,and moving the target to an acceptable location. The driver applies thenecessary corrections 603. As mentioned above, some trailer angledetection systems may not require the driver to attach a target to thetrailer during set up mode. The target and acquisition of the target aredirected to camera-based trailer angle detection systems.

When the target is acquired 614 by the trailer backup assist system andthe driver has acknowledged 616 the acquisition, the driver is thenprompted through a series of menus to input 620 trailer measurementinformation that may be stored in the trailer backup assist system for atrailer configuration that is to be associated with the named trailer.The next time the same trailer is attached to the vehicle, its uniquetrailer configuration will already be stored and progress through thesetup module will be faster or, in some cases, may be skipped entirely.Generic static images may be displayed at the HMI screen in order toassist the driver with the measurement information. Visual examples, seeFIG. 12, may be provided to aid the driver in identifying the locationon the vehicle, the trailer or between the vehicle and trailer that thedriver is being prompted to enter. In addition, numerical limits for thedriver entered measurements are set within the trailer backup assistsystem and may be displayed to the driver. The driver may be warnedabout entered measurements that exceed the numerical limits.Additionally, the measurement information requests that the driver isprompted to enter may be presented to the driver in the order that themeasurements should be entered into the trailer backup assist system.

It should be noted that while measurement information is discussed aboveas being entered by the driver, various methods of entering measurementinformation may also be employed without departing from the scope of theinventive subject matter. For example, a system to automatically detectmeasurements using existing vehicle and trailer data including, but notlimited to, vehicle speed, wheel rotation, steering wheel angle, vehicleto trailer relative angle, and a rate of change of the vehicle totrailer angle.

Examples of the measurement information may include a horizontaldistance from the rear of the vehicle to the center of a hitch ball, ahorizontal distance from the rear of the vehicle to a center of thetarget, a vertical distance from the target to the ground, and ahorizontal offset of the target from a centerline of the hitch ball. Inthe event the target is attached at other than the centerline of thehitch ball, then the trailer backup assist system must know which sideof the vehicle the target is attached to, the passenger side or thedriver side. A menu on the HMI may presented for the driver to indicatepassenger side or driver side for the placement of the target. Thetrailer backup assist system also needs to know the horizontal distancefrom the rear of the vehicle to a center of the axle or axles of thetrailer. The measurements may be entered in either English or Metricunits.

The driver is presented 622 with the option to revise any of themeasurements before proceeding with the setup process. Otherwise, thesetup module 600 is complete 624 and the calibration module 700 begins.

The calibration module 700 is designed to calibrate the curvaturecontrol algorithm with the proper trailer measurements and calibrate thetrailer backup assist system for any hitch angle offset that may bepresent. After completing the setup module 600, the calibration modulebegins 700 and the driver is instructed 702 to pull the vehicle-trailercombination straight forward until a hitch angle sensor calibration iscomplete. The HMI may notify 704 the driver, by way of a pop up orscreen display that the vehicle-trailer combination needs to be pulledforward until calibration is complete. When calibration is complete, theHMI may notify 704 the driver. Any hitch angle offset value is stored706 in memory, accessed as necessary by the curvature control algorithm,and the calibration module 700 ends 704.

It should be noted that while hitch angle calibration is described aboveas maybe requesting the driver pull forward information, various othermethods of hitch angle calibration may also be employed withoutdeparting from the scope of the inventive subject matter.

Upon completion of the setup module 600 and the calibration module 700,the activation module 800 may begin. The activation module 800 isdescribed with reference to FIG. 11. The activation module 800 isdesigned to activate automatic steering of the vehicle during trailerbackup assist operations. The driver is instructed 802 to place thevehicle in reverse. Upon activation of the trailer backup assist system,the steering system will not accept any steering angle commands from anysource other than the trailer backup assist system 804. The trailersetup 600 and calibration 700 modules must be completed and a currenthitch angle must be within a predetermined operating range for thetrailer backup assist system 806. The vehicle speed must also be lessthan a predetermined activation speed 808. In the event any one, or all,of these conditions 804, 806, 808 are not met, the driver is prompted toapply a corrective measure 810. The driver must confirm 814 that thecorrective action has been taken in order for the control module tobegin. If a corrective action is taken, but the activation module deemsit unacceptable, the driver will be instructed 810 to try anothercorrective action.

For steering systems where the steering wheel is directly coupled to thesteered wheels of the vehicle, the driver cannot engage with thesteering wheel during trailer backup assist. If any steering wheelmotion is obstructed, by the driver or otherwise, the trailer backupassist system will present instructions 810 to the driver to removetheir hands from the steering wheel. Activation 800 will be suspended ordiscontinued until the obstruction is removed. If the vehicle speedexceeds a threshold speed or if the vehicle hitch angle is notacceptable, the driver will be prompted 810 to take corrective action.Until corrective action is taken, accepted and acknowledged, theactivation 800 and control 200, 500 modules will be interrupted.

When the driver moves the gear shift from “park” to “reverse” 802 andpresses or turns a trailer backup steering input apparatus 125 a rearview camera image may appear in a display of the HMI. If at any timeduring the reversing process the hitch angle becomes too large for thesystem to control the curvature of the trailer, the TBA will provide awarning to the driver to pull forward to reduce the hitch angle. If atany time during the reversing process the system is unable to track thehitch angle target, the driver is presented with instructions to correctthe problem. If at any time the vehicle speed exceeds that predeterminedactivation speed, the driver is visually and audibly warned to stop orslow down.

When all of the conditions of the activation module are met andmaintained, the control module may begin. The control module executesthe directives described above with reference to FIGS. 5 and 7. However,the activation module 800 includes a monitoring function 816 so that, ifat any time during execution of the control module 200, 500 the controlis interrupted, the driver is instructed to make necessary corrections.In the event any one of the necessary corrections are not made, thecontrol of the vehicle by way of the trailer backup assist system willend. The driver may also intentionally end the control by exiting thesystem through a menu selection on the HMI or placing the vehicle in agear setting that is other than “park” or “reverse”.

Referring now to instructions processible by a data processing device,it will be understood from the disclosures made herein that methods,processes and/or operations adapted for carrying out trailer backupassist functionality as disclosed herein are tangibly embodied bynon-transitory computer readable medium having instructions thereon thatare configured for carrying out such functionality. The instructions aretangibly embodied for carrying out the method 200, 500, 600, 700 and 800disclosed and discussed above and can be further configured for limitingthe potential for a jackknife condition such as, for example, bymonitoring jackknife angle through use of the equations discussed inreference to FIGS. 5 and 7 and/or by implementing jackknifecountermeasures functionality discussed above in reference to FIG. 8.The instructions may be accessible by one or more data processingdevices from a memory apparatus (e.g. RAM, ROM, virtual memory, harddrive memory, etc.), from an apparatus readable by a drive unit of adata processing system (e.g., a diskette, a compact disk, a tapecartridge, etc.) or both. Accordingly, embodiments of computer readablemedium in accordance with the inventive subject matter include a compactdisk, a hard drive, RAM or other type of storage apparatus that hasimaged thereon a computer program (i.e., instructions) configured forcarrying out trailer backup assist functionality in accordance with theinventive subject matter.

In a preferred embodiment of the inventive subject matter, a trailerback-up assist control module (e.g., the trailer back-up assist controlmodule 120 discussed above in reference to FIG. 1) comprises such a dataprocessing device, such a non-transitory computer readable medium, andsuch instructions on the computer readable medium for carrying outtrailer backup assist functionality (e.g., in accordance with the method200 discussed above in reference to FIG. 2) and/or the method 500discussed above in reference to FIG. 8 and/or the methods 600, 700 and800 discussed above in reference to FIGS. 10 and 11. To this end, thetrailer back-up assist control module can comprise various signalinterfaces for receiving and outputting signals. For example, ajackknife enabling condition detector can include a device providinghitch angle information and hitch angle calculating logic of the trailerback-up assist control module. A trailer back-up assist control modulein the context of the inventive subject matter can be any control moduleof an electronic control system that provides for trailer back-up assistcontrol functionality in accordance with the inventive subject matter.Furthermore, it is disclosed herein that such a control functionalitycan be implemented within a standalone control module (physically andlogically) or can be implemented logically within two or more separatebut interconnected control modules (e.g., of an electronic controlsystem of a vehicle) In one example, trailer back-up assist controlmodule in accordance with the inventive subject matter is implementedwithin a standalone controller unit that provides only trailer backupassist functionality. In another example, trailer backup assistfunctionality in accordance with the inventive subject matter isimplemented within a standalone controller unit of an electronic controlsystem of a vehicle that provides trailer backup assist functionality aswell as one or more other types of system control functionality of avehicle (e.g., anti-lock brake system functionality, steering powerassist functionality, etc.). In still another example, trailer backupassist functionality in accordance with the inventive subject matter isimplemented logically in a distributed manner whereby a plurality ofcontrol units, control modules, computers, or the like (e.g., anelectronic control system) jointly carry out operations for providingsuch trailer backup assist functionality.

In the foregoing specification, the inventive subject matter has beendescribed with reference to specific exemplary embodiments. Variousmodifications and changes may be made, however, without departing fromthe scope of the inventive subject matter as set forth in the claims.The specification and figures are illustrative, rather than restrictive,and modifications are intended to be included within the scope of theinventive subject matter. Accordingly, the scope of the inventivesubject matter should be determined by the claims and their legalequivalents rather than by merely the examples described.

For example, the steps recited in any method or process claims may beexecuted in any order and are not limited to the specific orderpresented in the claims. The equations may be implemented with a filterto minimize effects of signal noises. Additionally, the componentsand/or elements recited in any apparatus claims may be assembled orotherwise operationally configured in a variety of permutations and areaccordingly not limited to the specific configuration recited in theclaims.

Benefits, other advantages and solutions to problems have been describedabove with regard to particular embodiments; however, any benefit,advantage, solution to problem or any element that may cause anyparticular benefit, advantage or solution to occur or to become morepronounced are not to be construed as critical, required or essentialfeatures or components of any or all the claims.

The terms “comprise”, “comprises”, “comprising”, “having”, “including”,“includes” or any variation thereof, are intended to reference anon-exclusive inclusion, such that a process, method, article,composition or apparatus that comprises a list of elements does notinclude only those elements recited, but may also include other elementsnot expressly listed or inherent to such process, method, article,composition or apparatus. Other combinations and/or modifications of theabove-described structures, arrangements, applications, proportions,elements, materials or components used in the practice of the inventivesubject matter, in addition to those not specifically recited, may bevaried or otherwise particularly adapted to specific environments,manufacturing specifications, design parameters or other operatingrequirements without departing from the general principles of the same.

The invention claimed is:
 1. A trailer backup assist system for use on avehicle having an attached trailer comprising: a human machine interfacedevice in communication with a controller; a setup module receivingtrailer measurements at the controller; a calibration module applyingthe trailer measurements to calibrate a curvature control algorithmassociated with the trailer backup assist system and to calibrate ahitch angle sensor associated with the trailer backup assist system; anactivation module for activating a steering system on the vehicle duringreverse movement of the vehicle-trailer combination; a trailer backupsteering input apparatus having a rotatable control element positionableat a zero curvature command position defined by backward movement of thetrailer along a substantially straight path defined by a centerlinelongitudinal axis of the trailer and positionable at positions withinopposing rotational ranges of motion relative to the zero curvaturecommanding position and generating driver request for a trailer pathcurvature command that is a function of at least one of an amount ofrotation of the rotatable control element with respect to the zerocurvature commanding position, a rate movement of the rotatable controlelement, and a direction of movement of the rotatable control elementwith respect to the zero curvature commanding position; and a controlmodule to receive the driver request, implement the curvature controlalgorithm, provide steering commands to the steering system to controlthe reverse movement of the vehicle-trailer combination in a mannerconsistent with the driver request, and implement a jackknifecounter-measure by altering at least one vehicle operating parameterthat increases a radius of a curvature path of the trailer and inhibitsa decrease in the radius of the curvature path of the trailer, thesteering commands during reverse movement of the vehicle-trailercombination are limited to those provided by the control module.
 2. Thesystem as claimed in claim 1 further comprising a plurality of menusdisplayed by way of the human machine interface device to assist withthe setup, calibration, activation and control modules.
 3. The system asclaimed in claim 2 wherein the trailer backup assist system furthercomprises: a target attached to the trailer; a first confirmationsignal, generated at the human machine interface device and communicatedto the controller, indicating the vehicle and trailer are in straightalignment with each other; a second confirmation signal, generated atthe human machine interface device and communicated to the controller,indicating that the target has been acquired by the trailer backupassist system; the trailer measurements being generated at the humanmachine interface device and received by the setup module only afterreceipt of the first and second confirmation signals by the controller,and a trailer configuration stored in a memory of the controller andbeing associated with the received trailer measurements.
 4. The systemas claimed in claim 3 wherein the setup module further comprises a menuselection displayed by the human machine interface device that providesan opportunity to revise the trailer measurements received by the setupmodule.
 5. The system as claimed in claim 3 wherein the setup modulefurther comprises a database containing a plurality of trailerconfigurations stored in a controller memory and displayed for selectionby the human machine interface device, the received trailer measurementsare retrieved from a stored trailer configuration selected from thedatabase.
 6. The system as claimed in claim 5 wherein the setup modulefurther comprises a menu selection displayed by the human machineinterface device that provides an opportunity to revise the trailermeasurements stored in the selected trailer configuration.
 7. The systemas claimed in claim 3 wherein the trailer measurements being received bythe setup module are being manually generated at the human machineinterface device.
 8. The system as claimed in claim 7 further comprisinga plurality of images stored in controller memory and displayed by thehuman machine interface device, each image is representative of adesired trailer measurement that is being requested for receipt by thesetup module and is presented in a predetermined order.
 9. The system asclaimed in claim 3 further comprising a display at the human machineinterface device instructing the driver to apply a corrective actionthat is required for at least one of the setup, calibration, activationand control modules.
 10. The system as claimed in claim 9 wherein thecorrective action is selected from the group consisting of: pulling thevehicle forward, cleaning the target, moving the target, replacing thetarget, cleaning a camera on the vehicle that is in communication withthe trailer backup assist system, pulling the vehicle forward, enteringor re-entering trailer measurements that are within a predeterminedrange, remove hands from a vehicle steering wheel, and reduce a speed ofthe vehicle.
 11. The system as claimed in claim 9 further comprising athird confirmation signal, generated at the human machine interfacedevice and received by the controller, indicating that the correctiveaction required by at least one of the setup, calibration, activationand control modules has been completed.
 12. The system as claimed inclaim 1 wherein the control module further comprises a monitoringfunction.
 13. A method for implementing a trailer backup assist systemon a vehicle having an attached trailer, the method carried out in acontroller associated with the trailer backup assist system andcomprising the steps of: receiving trailer measurements representativeof distances on the trailer, on the vehicle and between the trailer andthe vehicle; calibrating a curvature control algorithm and a hitch anglesensor associated with the trailer backup assist system in accordancewith the received trailer measurements; activating a steering system onthe vehicle after calibrating the curvature control algorithm and thehitch angle sensor; receiving a driver request to control reversemovement of the vehicle-trailer combination according to a desiredtrailer path curvature, the driver request being a function of an amountof rotation of a rotatable control element with respect to a zerocurvature commanding position defined by backward movement of thetrailer along a substantially straight path defined by a centerlinelongitudinal axis of the trailer, a rate of movement of the rotatablecontrol element, and a direction of movement of the rotatable controlelement; and implementing the curvature control algorithm to providesteering commands to the steering system in response to the driverrequest, the steering commands during reverse movement of thevehicle-trailer combination are limited to those provided by thecurvature control algorithm.
 14. The method as claimed in claim 13wherein the step of receiving trailer measurements further comprisesreceiving trailer measurements at the controller that are manuallygenerated at a human machine interface device in communication with thecontroller.
 15. The method as claimed in claim 13 wherein the step ofreceiving trailer measurements further comprises the steps of: receivinga first confirmation signal that a compatible trailer is attached;receiving a second confirmation signal that a vehicle is “on”; receivinga third confirmation signal that the vehicle is in “park”.
 16. Themethod as claimed in claim 14 wherein the step of receiving trailermeasurements further comprises the steps of: indicating, on the humanmachine interface device, a location of at least one trailermeasurement; and indicating, on the human machine interface device thatthe at least one trailer measurement, once received at the controller,is within or outside of predetermined boundaries.
 17. The method asclaimed in claim 15 wherein the step of receiving trailer measurementsfurther comprises the steps of: presenting at least one trailerconfiguration, stored in a controller memory, for selection by way ofthe human machine interface device; and receiving the trailermeasurements for a selected trailer configuration from the controllermemory.
 18. The method as claimed in claim 15 wherein the step ofcalibrating a hitch angle sensor further comprises the steps of:indicating to a driver of the vehicle, by way of the human machineinterface device, a need to pull the vehicle-trailer combination forwardto align the vehicle and the trailer; and indicating, by way of thehuman machine interface device, that the calibration of the hitch anglesensor is complete.
 19. The method as claimed in claim 13 wherein thestep of implementing the curvature control algorithm further comprisesimplementing a jackknife counter-measure by altering at least onevehicle operating parameter that increases a radius of a curvature pathof the trailer and inhibits a decrease in the radius of the curvaturepath of the trailer, the steering commands during reverse movement ofthe vehicle-trailer combination are limited to those provided by thecurvature control algorithm.
 20. The method as claimed in claim 19wherein the step of implementing a jackknife counter measure furthercomprises inhibiting a rate of change the driver request may bereceived.
 21. The method as claimed in claim 20 wherein the step ofinhibiting a rate of change the driver request may be received furthercomprises restricting an amount of rotation of a rotatable controlelement with respect to a zero curvature commanding position,restricting a rate of movement of the rotatable control element andrestricting a direction of movement of the rotatable control element.22. The method as claimed in claim 19 wherein the step of implementing ajackknife counter measure further comprises overriding a driver request.23. A trailer backup assist system on a vehicle having an attachedtrailer comprising: a human machine interface device in communicationwith a controller; a setup module for receiving trailer measurements atthe controller, a calibration module applying the trailer measurementsto calibrate a curvature control algorithm and a hitch angle sensorassociated with the trailer backup assist system; an activation modulefor activating a steering system on the vehicle during reverse movementof the vehicle-trailer combination; a rotatable control elementpositionable at a zero curvature command position defined by backwardmovement of the trailer along a substantially straight path defined by acenterline longitudinal axis of the trailer and at positions withinopposing rotational ranges of motion relative to the zero curvaturecommanding position, the rotatable control element generates a driverrequest as a function of at least one amount of rotation of therotational control element, a rate of movement of the rotatable controlelement and a direction of movement of the rotatable control element;and a control module to receive the driver request for a trailer pathcurvature command, implement the curvature control algorithm and providesteering commands to the steering system in response to the driverrequest to control the reverse movement of the vehicle-trailercombination in a manner consistent with the driver request, the steeringcommands during reverse movement of the vehicle-trailer combinationbeing limited by those provided by the control module.
 24. The system asclaimed in claim 23, wherein the control module is configured toimplement a jackknife counter-measure upon detection of a jackknifecondition, the jackknife counter-measure includes at least one ofreducing a speed of the vehicle, increasing a radius of curvature of apath of the trailer, and inhibiting a decrease in the radius of thecurvature of the path of the trailer.
 25. The system as claimed in claim24 wherein the jackknife counter measure further comprises affecting therotatable control element to restrict an amount of rotation of arotatable control element with respect to a zero curvature commandingposition, restrict a rate of movement of the rotatable control elementand restrict a direction of movement of the rotatable control element.